1. Field of the Invention
The present invention relates to a method and an apparatus for addition data transmission and reception in a digital broadcast system, and more particularly, to an apparatus and a method for transmitting addition data while maintaining backward compatibility with existing broadcast data in a digital broadcast system.
2. Related Art
In general, in an existing broadcast system, data transmission rate is determined according to each standard. For example, data transmission rate of an advanced television systems committee (ATSC) 8-vestigal sideband (VSB) transmission standard is 19.39 mbps in a band of 6 MHz, data transmission rate of a digital video broadcasting-terrestrial (DVB-T) transmission standard is 4.354 Mbps to the minimum to 27.710 Mbps to the maximum in a band of 7 MHz, and data transmission rate of a terrestrial-digital multimedia broadcasting (T-DMB) transmission standard is generally 1.125 Mbps in a band of 1.536 MHz.
Due to development of various services and culture contents, new-concept services such as data broadcasting, a non-real time (NRT) service, a disaster alert service, a public infra control, and the like are emerged and necessity of transmission of additional services are presented. In the existing broadcasting and communication system, a method, which allocates new services to transmission rate of remaining data by reducing data transmission rate of an original service is used in order to additionally provide the new-concept services. For example, in the ATSC 8-VSB system, approximately 2 Mbps is allocated for the new service such as the data broadcasting in 19.39 Mbps allocated for HD broadcasting and existing HD broadcasting is reallocated to remaining 17.4 Mbps. In the related art, since the data transmission rate of the original service is decreased in order to additionally transmit the new services, the quality of the original service deteriorates.
Therefore, in the broadcast system in the related art, a method is urgently needed, in which transmission rate of existing data is maintained, that is, backward compatibility with the existing broadcast system is maintained and addition data are additionally transmitted to increase transmission efficiency, and various methods are proposed for this.
First, in the ATSC system, a method is presented in prior art, which can transmit addition data by using a polarity and an amplitude level of a transmitter identification (TxID) signal used to configure a single frequency network (SFN).
In an existing TxID based addition data transmission method using the polarity and the amplitude level, the addition data can be transmitted through the TxID signal while a transmitter identification function as an original object of the TxID signal is maintained. However, the method using the polarity and the amplitude level in the related art has a problem in that transmission rate (tens to hundreds bps) is very low.
In order to complement the problem that the transmission rate is very low, a method for addition data transmission by using a phase and a polarity of a TxID sequence and a method for addition data transmission by combining an additional orthogonal sequence and the TxID signal are presented in prior art. In the presented methods, the addition data of several Kbps can be transmitted.
The presented method for addition data transmission based on the TxID signal has advantages to transmit the addition data of hundreds bps to several Kbps while maintaining backward compatibility with the existing digital broadcast system. However, since the existing DTV signal and TxID signal are combined before modulation, a modulator of a transmitter without a TxID function, which has already been installed needs to be replaced. Moreover, since the performance of an addition data receiver, particularly, the performance of a demodulation unit including a synchronous unit fully depends on the demodulation performance of the existing DTV signal, the addition data is not detected at a low signal to noise ratio (SNR). The method for addition data transmission based on TxID is very vulnerable to a multi-path signal and is impossible to perform mobile reception.
Accordingly, an apparatus and a method for addition data transmission are keenly required, which can ensure excellent reception performance in at the low SNR and under a multi-path environment while maintaining backward compatibility with the existing broadcasting signal without changing the existing digital broadcast system.